Along with the advances in high density recording and capacity increase with respect to magnetic storages or memories, which are represented by magnetic disk devices (hard disks) and magnetoresistive random access magnetic memories (MRAM) that use magnetic materials, utilization of perpendicularly magnetized films that are magnetized in the direction perpendicular to the film plane is effective. For the increase in the recording density induced by miniaturization of the recording media for hard disks using this perpendicularly magnetized film or magnetic tunnel junction elements (MTJ elements) that constitute the recording bits of MRAM, it is necessary to increase the magnetic anisotropy energy density Ku through quality improvement of the perpendicularly magnetized film. Also, in order to obtain a perpendicularly magnetized film with superior quality, the presence of an underlayer that takes an important role in the control of the crystal orientation or the crystal grain size, reduction of stacking faults, and securing of flatness, is extremely important.
Non-Patent Literature 1 discloses that in perpendicular magnetized recording media of Co-based alloys such as a cobalt-platinum-chromium (Co—Pt—Cr) alloy or the like, a Ru underlayer having a hexagonal close packed (hcp) structure is used, which has the same crystal structure as these alloys do. Furthermore, in regard to a L10 type iron-platinum (FePt) alloy that is expected to be applied to recording media or MTJ elements of the future because a very high Ku may be obtained, Non-Patent Literature 2 discloses magnesium oxide (MgO) having a sodium chloride structure (NaCl structure) as an effective material for an underlayer for the alloy, while Patent Literature 1 discloses magnesium-titanium oxide (MgTiOx).
Furthermore, in a perpendicularly magnetized film for exclusive use in a MTJ element, perpendicular magnetization can be realized even for soft magnetic materials such as cobalt-iron-boron (CoFeB) or iron (Fe), which do not exhibit perpendicular magnetization in a bulk state, when the interface effect of an ultrathin film structure is utilized. Therefore, it has been suggested that the perpendicularly magnetized film can be used as a recording layer (interface-induced perpendicularly magnetized layer). In this case, according to Non-Patent Literatures 3 and 4, a microcrystalline material or a body-centered cubic (bcc) structure-based material, such as tantalum (Ta) or chromium (Cr), is utilized as an underlayer.
However, the above conventional L10 type alloys and MgO underlayers have lattice mismatch at a proportion of close to 10%, and a flat film form having high crystallinity and high degree of order cannot be realized. Furthermore, the underlayers for conventional interface-induced perpendicularly magnetized layers have poor heat resistance, and have a problem that the heating treatment necessary for securing the tunnel magnetoresistance (TMR) ratio of a MTJ element cannot be implemented. Also, some of ferromagnetic materials are subjected to the influence of distortion by the underlayer, and therefore, it is made impossible to extract sufficient characteristics. Therefore, it has been hitherto difficult to enhance the product quality of magnetic recording media or MTJ elements, which use these perpendicularly magnetized films.